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  • John Carbone
  • November 20, 2009
  • 11:37pm

I think Tom nailed it. We have many customers using the first approach (Asymmetric Multi Processing, or AMP) exactly as Tom described. In such systems, performance gains can be pretty close to 2x (in a dual-processor syetem), compared to running both functions on the same processor. In theory, depending on how efficient each implementation is, even more than 2x can be achieved - if the single-processor approach involves a lot of context-switching between the functions (thrashing), adding significant overhead. In the AMP approach, it's possible that much of the context switching can be eliminated. Countering that, though, is the added "overhead" of communication across processor boundaries. The amount of that can significantly affect performance and possibly take a 2x gain down lower. As far as Symmetric approaches (Symmetric Multi Processing, or SMP), there seems to be a tradeoff of ease of implementation versus performance. In SMP, while implementation is easier than AMP, and sometimes even close to automatic, there is more likely to be overhead induced by multiple processors accessing common memory. If this can be avoided, and the processors enabled to run on their own continuously for significant periods of time, then on a 4-processor system, performance can indeed approach 4x. But, this is extremely rare and pehaps even unrealistic, so I wouldn't expect to achieve it most of the time. Undoubtedly, the simplest answer to your question is that performance gain is extremely application dependent. Quite likely, the more effort you're willing to invest, the closer you can get to your ultimate performance goal.

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